Logging methods and apparatus have been proposed which may be used when a drill stem is in a bore hole and may be used at any time with a minimum of interruption in drilling. In accordance with these methods, a self-contained energizing and recording apparatus may be dropped through a drill stem in a go-devil fashion or may be pumped down therethrough when the drill stem has been lifted to only a limited extent from the bottom of the hole to provide a region for reception of an electrode or other logging assembly. The apparatus particularly includes an assembly of a type suitable to pass through the mud flow openings of a jet bit which may be of any of the conventional types. These openings are generally at relatively small angles with respect to the drill stem axis, and a flexible assembly may, accordingly, be projected therethrough to extend beneath the bit.

The self-contained assembly lowered into the vicinity of the bit contains, for electrical logging, not only means for supplying current to the earth, but also means for recording various potentials appearing at the electrodes of the assembly.

According to the prior method, a catcher ring is provided in the drill stem in the joint between the drill stem and the sub-assembly immediately above the drill bit. This catcher ring is engaged by a portion of the logging apparatus descending through the drill stem and serves to position the same at the desired logging location. It is an object of the present invention to provide a logging apparatus of the indicated type which may be used in a drill stem which does not have a catcher ring. In accordance with the present invention such means comprises an extension on the casing containing the energizing and recording apparatus which extension is contactable with the drill bit to position the apparatus.

Another object ofthe present invention is to provide a mud pressure rise indication when the logging instrument has been located at the bottom of the drill stem in position for logging.

Another object of this invention is to provide a means for cushioning the impact of the logging assembly when its downward movement is arrested.

A still further object of this invention is to electrically arm the logging apparatus at a predetermined time after this apparatus has been located at the bottom of the drill stern. This is advantageous since the saving of the battery power is important and it is thus desirable to draw power only when the apparatus is ready to function, i.e. when located at the logging position at the bottom of the drill stem. In the prior logging methods and apparatus, a time delay circuit is grounded immediately before the apparatus is lowered through the drill stem. This grounding is effected `by grounding one of the electrodes, generally the current electrode, which is temporarily connected in the controlling circuit. The time delay is set to initiate the logging only after the logging assembly has reached the bottom of the drill stem. Hence, the time delay must be set in accordance with an approximation of the time of descent. It is important that this time delay be comfortably in excess of the time of descent to be absolutely certain that the logging apparatus has reached the logging position at the bottom of the drill stem before logging is started. Thus, the time delay is set at a period which is generally much longer than is actually required.

In accordance with the present invention, a switching means, which is connected within the control circuit, is actuated to start the time delay immediately upon the logging assemblys reaching th'e bottom of the drill stem. rThus, a much shorter arming time may be used because the time delay in accordance with the present invention may be set to a very short period since there is no need to approximate the descent time. Moreover, in the method in accordance with this invention, there is no danger of arming the logging apparatus: before it has reached the logging position.

The above and other objects and features of the invention will become apparent from a consideration of the following description taken in conjunction with the accompanying drawings wherein:

FIGURE lA is a vertical section of the landing and arming means in accordance with this invention illustrating the position of the parts as the apparatus descends through the drill stern;

FIGURE 1B is a continuation of the electrode assembly shown in FIGURE 1A;

FIGURE 2 is a vertical section of the landing and arming means shortly after contact thereof with the drill bit;

FIGURE 3 is a vertical section of the landing and arming means illustrating the position of the parts a` period of time after landing;

FIGURE 4 is a wiring diagram showing, in particular an electrical control and power assembly; and

FIGURE 5 is a diagram illustrating the logging electrical system and its connection to the power and control assembly.

The logging assembly which is lowered through the drill stem 10 comprises a housing 11 which is of considerable length and serves to house the electrical apparatus necessary for logging. A pair of plugs 12 and 14 are secured to housing 11 at the upper and lower ends thereof by suitable means such as plug members 15. Plug members 16 are axially movable and are arranged to be received in openings in housing 11. Supported between the plugs 12 and 14 is an electrical energiz'ing and recording apparatus indicated generally at 1S. The energizing and recording apparatus may be of the type described in the copending application of Fred M. Mayes and I ack Weir Jones, Serial No. 818,066, filed June 4, 1959. Since the construction of the logging apparatus forms no part of this invention, further de'- scription thereof is deemed unnecessary, particularly since the details of construction thereof are fully disclosed in said prior mentioned application. Plugs 12 and 14serve as a closure means to seal the logging apparatus from contact with the drilling mud as is more fully described in the copending application of Preston E. Chaney, Serial No. 818,161, tiled June 4, 1959, now Patent No. 3,074,- 589.

An electrode assembly is supported beneath plug 14 and comprises an adaptor 2t) Within which are mounted pins 22 electrically connected to the electrode leads. In accordance with this invention, one of the pins 22 may be connected to a Contact member 24 mounted lon the exterior trical cable on which electrodes are provided. The electrode assembly will be more fully described hereinafter.

The landing and arming means in accordance with this invention includes a tubular extension member indicated generally at 29 extending downwardly from housing 11 and comprising an upper section 30 threadedly engaging plug 14, a lower section 32 providing the lower end of the landing and arming means and a medial section 34 interconnecting sections 30 and 32. Medial section 34 is made of a flexible material, such as rubber, and has the ends thereof reinforced by fabric, as at 35, to reduce the flexibility of these ends. The ends of section 34 are received within suitable recesses in sections 30 and 32 and are constructed with a diameter such that there is a tight frictional t between the ends of section 34 and sections 30 and 32. The medial portion of section 34 has a thickness greater than the ends thereof and has a barrelshaped inner wall. It will thus be apparent that sections 30 and 32 are axially movable relative to each other by a ilexure of medial section 34. With the lower section 32 resting on a supporting structure, such as 4a drill bit, the medial section is capable of supporting the weight of the apparatus thereabove without bowing enough to touch the drill stem wall for a purpose more fully explained hereinafter.

Positioned within tubular extension 29 is an elongated member 36 which is secured to section 30 by a plug member 38. Plug member 38 is of well-known type of securing means and has a stem threaded into a threaded bore in member 36 and a head movable in a counterbore therein. Plug 38 is axially movable upon rotationthereof to be received in a bore in section 30 in axial alignment with the counterbore in member 36. By this construction, member 36 may be secured to section 30 within any projection of elements beyond the outer diameter of section 30.

- The lower portion of member 36 extends through a bore 39 in a partition 40 in section 32. The lower end of member 36 which projects beneath partition 40 has an annular member 42 secured thereon. As is best shown in FIGURE lA, member 42 serves to limit the axial movement ofsection 32 away from sections 30 and 34 by contact with the lower wall of partition 40.

Member 36 has an axial bore 44 adapted to contain therein the upper portion of sheath 28 of the electrode assembly exending from adaptor 20. The portion of section 32 beneath partition 40 is tapered at 46 and has an opening 48 therein. The sheath 28 thus extends from adaptor portion 20, through bore 44 and opening 48, and downwardly through the drill stem 10.

Extending downwardly from the lower end of tapered portion 46 is a rod 50. Rod 50 has an enlarged head 52 at the lower end thereof adapted to engage the usual shoulder 54 of a drill bit 56 (see FIGURES 2 and 3). The rod 50 is of a predetermined definite length so that the logging apparatus rests on the drill bit shoulder 54 in a definite vertical relationship with respect to the drill bit.

The dril1 bit 56 may be of any of the conventional types having mud ow jet openings as at 58. Such bits are presently widely used since they effect the carrying away of cuttings and avoid their reworking by the drill. The jet openings 58 are generally at a relatively small angle with respect to the drill stem axis and the flexible electrode assembly may, accordingly, be projected therethrough to extend beneath the bit. The jet openings 58 are usually provided with erosion-resistant liners 59.

Within extension 29 is an annular chamber 60 dened by partition 40, member 36 and the inner wall of extension 29. Mounted for slidable movement in chamber 60 on the exterior of member 36 is a tubular piston member 62. Piston member 62 has enlarged head portions 64 and 66 at the upper and lower ends thereof, respectively. Piston member 62 is axially movable between a shoulder 68 formed on member 36 and the upper wall of partition 40. A switch arm 70 is mounted on the upper end of piston 62 to extend into a cavity 71 in the upper portion of member 36 for contact with the contact member 24. To insure that arm 70 is maintained in alignment with Contact member 24, means are provided to prevent rotatable movement of member 62 relative to member 36. Such means may comprise suitable key members (not shown) or cavity 71 may have the same width as arm 70. Arm 70 is connected to ground through an electrical path comprising member 62, member 36, section 32, extension 5t) and dril1 bit 56.

The outer diameter of the head portions 64 and 66 are constructed to frictionally contact the inner diameters of sections 30 and 32, respectively, and the inner diameter of the ends of section 34. By reason of the frictional contact between member 62 and tubular extension 29 at heads 64 and 66, axial movement of piston member 62 is retarded. Thus, member 62 will be frictionally retained in any axial location within tubular extension 29 at which it is positioned or actuated.

A pair of longitudinally spaced openings 72 and 74 are provided in the wall of tubular extension 29 to provide passageways for communication between chamber 60 and the exterior of extension 29. Opening 72 is located near the upper end of medial section 34 and opening 74 is located near the lower end of medial section 34. Openings 72 and 74 and chamber 60 thus deline a passage by-passing the exterior of section 34. A restricted orifice 78 is provided to provide a passageway extending from the upper wall of partition 40 to the exterior of tubular extension 29. Head 66 has a tapered orifice 82 between the lower end thereof and a side thereof in alignment with opening 76 for a purpose to be hereinafter described.

The openings 72 and 74 are spaced a distance slightly less than the spacing between the inwardly facing ends of heads 64 and 66. When the piston member 62 is in the upper position shown in FIGURE lA, head 66 closes off chamber 60 at a location between openings 72 and 74 to prevent flow therebetween. Partition 40 is spaced beneath opening 74 a distance approximately equal to the length of head 66. Thus, in the lower position of piston member 62, shown in FIGURE 3, the upper end of head 66 is beneath opening 74 to permit flow between openings 72 and 74 through chamber 60.

The electrode assembly and the electrical logging circuitry herein involved are to a considerable extent, similar to that of the prior-mentioned application of Mayes and Jones.

As has already been indicated, the electrode assembly is fundamentally a multi-conductor insulated electrical cable on which electrodes are provided. There may be used any number of conductors corresponding to the number of electrodes or other requirement. Any number of electrodes may be provided as indicated at 128, and 132, each being conneced to an individual conductor of the cable. While many electrode configurations may be used as will become evident, the following description will be consistent with the use ofl three electrodes such as are indicated in the drawings. The lowermost electrode 128 is the current electrode through which current is introduced into the earth, the next electrode 130 being typically about 16 inches from the first electrode 128 and being known as the short normal electrode, while the third electrode 132 may be typically about 64 inches from the current electrode 128 and is known as the long normal electrode, serving also as a self-potential electrode. These electrodes are quite remote Afrom the lower end of the supporting assembly and the adaptor. They may, for example, be of the order of 20 feet or more distant from this adaptor and correspondingly distant, during use, from the drill bit immediately above which the protective housing rests during operation. It may be noted that the particular electrode arrangement is rather arbitrary and that other arrangements may be used. For example, the self-potential electrode may be any of the three shown, or a separate self-potential electrode may be provided.

At the lower end of the electrode assembly there is the weighting arrangement shown particularly in FIG- URE 1B. A coupling at 126 supports a flexible wire cable 127 terminating in a stop member 129 there being threaded on the cable 127 a series of lead weights 131 with rounded upper and lower ends with interpositions between pairs of these weights of flexible washers 133 which may be made, for example, of neoprene. A sufiicient number of the weights is used to insure that during lowering the flexible electrode assembly will remain under tension. The arrangement just described provides the necessary flexibility to enable the entire assembly to pass through the jet bit openings, At the same time there is provided an arrangement which cannot hang up on tool joints or shelves in the wall of the hole below the bit. The washers 133 maintain the outside diameter of the weighting arrangement to prevent engagement of the depression between the weights from being arrested by the lower edges of the jet opening during removal of the electrode assembly. A exible strip 135 of leather or plastic extends from the stop member 129 and facilitates, by its entrainment in the mud flow, the guidance of the electrode assembly into a jet opening in the bit.

The overall arrangement of the electrical portions of the apparatus is shown in FIGURE 5. The electrical power and control assembly is shown in detail in FIG- URE 4.

The power and control assembly comprises a main power supply battery 214 having its negative terminal grounded and its positive terminal connected through the series arrangement of a switch 144 and a manually closable switch 212 to a terminal 216. Switch 212 is a limit switch which is opened and closed by the adjustment of a timer 181 connected to a time delay motor 182, the switch 212 being closed when the timer is adjusted from its zero position to a time delay setting. The terminal 216 is connected to the upper end of the winding 218 of a relay, this winding being shunted by a capacitor 221i. Interposed between the lower terminal of this winding and the ground is a resistor 222 in series with the switch 148 which is normally open so long as there is recording tape on the recording tape supply reel. The lower end of the winding 218 is also connected to the movable contact 224 of the relay which selectively engages the fixed contacts 226 and 228, the former being engaged when the relay is deenergized. The terminal 216 is connected through resistor 230 to provide current for the drive of the time delay motor 182, the return from this motor being to the lower fixed contact 238 engageable by the grounded movable contact 234 of the relay just mentioned, this movable contact being, when the relay is deenergized, in engagement with the upper iixed contact 236. The resistor 230 also supplies current to one terminal of the recorder motor 172.

The motor 182 is operatively connected to the timer 181 to drive the same upon motor energization. The timer 181 is operatively connected to switch 206 in a suitable manner, such as is schematically indicated by the connection 183. Timer 181 is operative through connection 133 to close the switch 266 upon expiration of a time delay set at the timer 181. One form of such arrangement would comprise a feed screw driven by motor 132 and having a nut mounted thereon for axial movement in response to screw rotation and means movable by the nut to contact the switch 206 to close the same, the nut being disengageably mounted on the feed screw to permit axial adjustment for setting the time delay. However, any suitable timing means and connection may be provided. The switch 206 connects the terminal 216 to the terminal 232 from which the power control assembly is connected to the electrical logging circuitry which comprises, as is described on said Mayes and Jones application, an oscillator, a self-potential recorder, a long normal recorder and a short normal recorder.

A second relay has a winding 241) and associated with it are the movable contacts 242 and 248. When the relay is energized, contact 242 engages the tixed contact 244 which is connected to the other terminal of motor 172, the movable contact 242 being connected at 246 to the fixed contact 236 of the relay 218. The movable contact 248 is connected to ground through a switching means indicated at 251 and comprising the contact member 24 and the grounded switch arm 70. When the relay 241% is deenergized, the movable contact 248 engages the xed contact 25) which is connected at 252 to the fixed contact 226 of the relay 21S. The upper terminal of the second relay winding 240 is connected at 258 to a fixed Contact 260 engageable by the movable contact 262 of a third relay having a winding 261, the upper terminal of which is connected to the positive supply terminal 232. The movable contact 262 is connected at 264 to the lower terminal of this relay winding. A second movable contact 266 of the third relay is grounded and is arranged, when the relay is deenergized, to engage the lixed contact 268 which is connected at 270 through the resistor 272 to the lower iixed contact 228 of the first relay. A transistor 274 has its collector connected to the lower end of the Winding 261, its base connected to the contact 278 through the connection 276 and its emitter to the iixed switch contact 280 engageable by the grounded switch arm 210. The switch arm 210 :alternatively engages the tixed contact 282 which is connected to the transistor base and also to a terminal 284 for connection to the electrical logging circuitry as is indicated in FIG- URE 5.

`FIGURE 5 illustrates the interconnection between the power and control assembly and the electrical logging circuitry. The power and control assembly is connected to the electrical logging circuitry at terminals 232 and 284 and to ground through switch 251. The details of the preferred form of electrical logging circuitry are described in said Mayes and `Tones application. The electrodes 128, 131) and 132 are, of course, connected to the recorders of the logging circuitry as is more fully described in said Mayes and Jones application.

In the apparatus disclosed the saving of battery power is important and, consequently, it is desired to draw power only when the apparatus is ready to function. This is accomplished by reason of the control feature of the switching means 251 comprising contact 24 and switch arm 70 in a manner to be more fully described hereinafter.

The overall operation of the apparatus will now be described.

Preliminary assembly at the surface requires that the magnetic tape be in condition to feed, and this involves an open condition of the switch 14S. The timer 181 for determining the amount of the time deiay of motor 182 is then set, the setting being such as to initiate the record- -ing operation after a short time interval, approximately four minutes, following the initial triggering after the instrument has reached the bottom of the drill stem with the electrode assembly extending below the bit through a jet opening. The setting of the timer 181 will automatically effect closure of the switch 212 but initially this has no etfect in the starting operation. The operating assembly is then placed in the protective casing provided by the tube 11 to cause closure of switch 144 as described in said Mayes and iones application.

With the drill stem lifted from the bottom of the hole to provide a space for extension of the electrode assembly below the bit, the assembly is ready for lowering. As already indicated, the apparatus may be dropped in godevil fashion, may be lowered on a wire line, or may be pumped down through the drill stem. Its -descent through the drill stem is retarded by a retarding means such as that disclosed in said Mayes and Jones application. Ultimately, the electrode assembly will enter and feed through the jet opening in the bit by entrainment in the drilling mud, with the apparatus finally coming to rest with the electrode assembly fully extended and with a good, low resistance ground connection being made at the bottom of the drill stem by engagement of rod 50 with the bit.

As the assembly is lowered through the drill stem, the parts of the landing and arming means are in the position shown in FIGURE 1A. During the descent of the assembly, drilling mud is continuously pumped down through the drill stem as indicated by the arrows in FIGURE 1A. The piston member 62 is in the uppermost position with head 64 engaging shoulder 68. In this position, the contact head of the switch arm 70 is above the contact member 24 whereby the switching means 251 is open. The drilling mud will be contained in the portion of chamber 60 above head 66 by reason of opening 72 and will be contained within the portion of chamber 60 beneath head 66 by reason of tapered orifice 82 and restricted orifice 78 so that the pressure on both sides of head 66 will be the same. Also, since the cavity 71 communicates with the exterior of the extension 29 by way of passageway 84, the pressure on both sides of head 64 will be the same. Thus, piston member 62 will remain in the position shown in FIGURE 1A as the assembly descends. Also section 32 will be supported from section 30 by member 36 at collar 42 so that section 34 will be in its elongated position permitting the unrestricted flow of the drilling mud past the exterior thereof.

Subsequently, the head 52 of rod 50 will engage the drill bit shoulder 54 and the descent of section 32 will be arrested. Immediately after this arresting, the weight Ving the drill stem wall, the landing impact causes the above-described bowing movement. It will be apparent that this bowing movement of section 34 tends to cushion the landing impact of the assembly. When this bowing occurs, the drilling mud being pumped downwardly through the drill stem cannot pass the medial section 34 either exteriorly thereof by reason of the contact between member 34 and drill stem 10 or by way of the passageway 60 by reason of the interference by the head 66 of piston member 62. Thus, there will be a mud pressure rise indication at the pumping means on the surface of the well by reason of the backing up of the drilling mud. Also, there will be an increase in the mud pressure above the location at which the section 34 has shut off the flow of mud. This increased pressure will be transmitted through opening 72 into chamber 60 which will provide a pressure on the upper side of head 66 greater than the pressure beneath the head 66. By reason of this pressure differential across head 66, piston member 62 will be forced downwardly. In the initial portion of the downward movement of piston member 62, the drilling rnud in chamber 60 beneath head 66 will be forced outwardly thereof through both the passageway provided by tapered orifice 82 in cooperation with opening 74 and the passageway provided by restricted orifice '78. The member 34 will be maintained in this outwardly bowed position by reason of the differential pressure between chamber 60 and the exterior of member 34 below the sealing area.

It will be apparent that as the piston member 62 moves downwardly across opening 74, tapered orifice 82 cooperates with opening 74 to progressively diminish the size of the opening through which the mud may escape from the portion of chamber 60 beneath head 66 through the passageway provided by tapered orifice 82 and opening 74. The diminishing of this passageway opening will tend to progressively reduce the rate at which the mud may be forced out of the portion of chamber 60 beneath head 66 to thereby tend to decrease the rate of downward movement of piston member 62. Since the piston member 62 will thus prevent flow between openings 72 and 74 for a longer time period, there will be a larger pressure build-up to thereby provide a good mud pressure rise indication at the pumping means. When the piston member 62 reaches the position shown in FIGURE 2 wherein the tapered orifice 82 is closed by cooperation with the inner wall of section 32, the descent of the piston member 62 will be slowed down to a minimum since the only outlet passageway from the portion of chamber 60 beneath head 66 will be through restricted orifice 78. It will thus be apparent that orifice 82 serves to control the pressure build-up.

As shown in FIGURE 2, the parts are constructed and arranged so that the switch arm 70 will engage contact 24 during the initial portion of the minimum rate of downward movement. This construction insures that the period of engagement of arm 70 with contact 24 is sufficient to provide good switching contact.

Engagement of arm 70 with contact 24 completes a control circuit which may be used to eventually effect initiation of the recording apparatus after a short time delay as Will be more fully described hereinafter. Continued downward movement of piston member 62 will break this contact. However, in accordance with the control circuit herein involved, only momentary closing of the switching means is required.

As the piston member 62 continues to descend by reason of the pressure differential, the upper side of head 66 will move beneath the opening 74 to permit the passage of drilling mud through opening 72, chamber 60 and opening 74 to the exterior of medial portion 34 at the location beneath the contact area between the bowed medial portion 34 and the drill stem 10. Thus, the pressure on both sides of the section 34 will equalize. Since medial portion 34 is capable of supporting the apparatus above it without bowing enough to contact the inner wall of drill stem 10, the medial section 34 will move inwardly to its elongated position and raise the upper section 30 and the member 44 upwardly to the position shown in FIGURE 3. Thus, the drilling mud may liow without restriction past the medial section 34 as is indicated by the arrows in FIGURE 3. FIGURE 3 also illustrates the final position of the piston member 62 with the lower end of head 66 contacting partition 40.

The operations of the controlling apparatus are as follows:

The grounding of the contact 248 by the action of the switching means 251 energizes the relay 218 through the connections 248, 250, 252, 226 and 224, grounding the lower terminal of the relay winding. This occurs, as was described above, when the recording apparatus has reached the bottom of the drill stem. A note of this time may be made since there will be an indication at the surface as was described above of this position of the recording apparatus. Correlation of time at the surface with the original setting of the time delay will indicate to an operator when the apparatus is ready to start logging. This will normally be four minutes after the apparatus has reached the bottom of the drill stem. A time log is kept recording the particular times when lengths of drill stem are disconnected and removed during the logging operation. The relay 218 is self-locked by the engagement of movable contact 224 with fixed contact 228 which completes a grounding circuit through resistance 272 and through contacts 268 and 266. The grounding control circuit through switch 251 and contact 248 is simultaneously opened at 226. Engagement of contacts 234 and 238 completes a ground to the circuit of timing motor 182.

The next event which occurs after the timing interval which has been preset is the closure of switch 206 by the action of the time delay motor 182 through timer 181 and connection 183. This closure of switch 206 connects the positive terminal of the battery 214 to the main supply terminal 232 of the various transistor circuits of the circuit elements. Additionally, the closure of switch 266 provides current supply to the upper termlnal of the relay winding 26l. No action occurs at this time since the switch 214% is in the position illustrated, opening the emitter circuit of the transistor 274.

Subsequently, the shifting of the switch 21d occurs to engage the terminal 280 and thus ground the emitter of the transistor 274. The transistor is now ready to respond to a signal through terminal 284, such signals being emitted from a recording circuit of the electrical logging circuitry as is described in said Mayes and Jones application.

The occurrence of a signal at 284 effects the following operations:

Relay Zei is energized and locked `by Contact of 262 with 260 in series with the relay 240. Contacts 266 and 273 ground the base of transistor 274 and also the terminal 284 which is at the lower end of the recording head coil. Thus, this coil is put into the same electrical condition as the coils of the other recording circuits of the electrical logging circuitry.

The opening of engagement between contacts 266 and 2.63 deenergizes the relay Zl. The release of contact 234 stops the timing motor 182. At the same time, contacts 234 and 236 engage and 242 and 244 are closed to start the recording motor i172.

At this time all of the elements of the apparatus are in condition for logging, and recording is accomplished in the manner more fully described in said Mayes and Jones application. Logging will generally be carried out by raising the drill stem, section by section, though, of course, a checking log may be provided by thereafter lowering the drill stem.

It will be evident that various details of construction and operation may be modified without departing from the invention as defined in the following claims.

What is claimed is:

1. In apparatus for the logging of bore holes, the combination comprising a housing adapted to be lowered through a drill stem carrying a drill bit in a bore hole, logging apparatus within said housing, a casing mounted on the lower end of said housing having an expandible section movable between a position allowing the ow of a fluid through the interior of the drill stem and a position in contact with the inner wall of the drill stem to block such uid ow, means attached to said section to urge the same to its non-expanded condition for maintaining said section in said ow allowing position when the housing is lowered through the drill stem, means bypassing said section including a chamber in said casing and a pair of passageways communicating with the exterior of said casing and said chamber above and below said section, respectively, said drill bit having landing means for engaging the casing, said casing having a bit engaging means below said section, the portion of the casing above said section being movable downwardly with respect to the bit engaging means upon engagement thereof with said landing means to move said section to said flow blocking position, a piston member in said chamber movable from a position blocking flow between said passageways to a position permitting fiow between said passageways in response to the pressure build-up of the fluid flowing in the drill stem when said section has moved to said position thereof blocking the iiow of fluid, and means connected to said piston member responsive to movement of said piston member from said flow blocking to said iiow permitting position for effecting a control operation of said logging apparatus.

2. Apparatus as claimed in claim 1., wherein said logging apparatus control means comprises a control circuit for said logging apparatus, switching means connected in said control circuit for making and breaking the same, said switching means having a switch contact mounted for movement through a switching movement to change the condition of said control circuit, and means interconnecting said switch contact and said piston member for actuating said switch contact through said switching movement thereof in response to said movement of said piston member.

3. Apparatus as claimed in claim 1 wherein said piston member is positioned to intersect said chamber at a location between said pair of passageways when said piston member is in said flow blocking position with one side of said piston member being responsive to they iow of fluid through one of said passageways and the other side of said piston member being responsive to the ilow of iiuid through the other of said passageways, said piston member being movable across said one passageway upon movement from said ow blocking to saidiiow permitting position, said piston member being positioned beyond said one passageway in said flow permitting position whereby said pair of passageways are in communication through said chamber.

4. Apparatus as claimed in claim 3 including passageway means interconnecting the portion of said chamber communicating with said one side of said piston member with the exterior of said casing for equalizing the pressures on said both sides of said piston member when said section is in said flow allowing position.

5. Apparatus as claimed in claim 4 wherein said passageway means includes a third passageway interconnecting said portion of said chamber communicating with said one side of said piston member with the exterior of said housing and a fourth passageway in said. piston member and communicating with said one passageway during a portion of said piston member movement to interconnect said one passageway with said portion of said chamber communicating with said one side of said piston member.

6. Apparatus as claimed in claim 5 wherein said third passageway has a restricted orifice and said fourth passageway communicates with said one passageway during movement of said piston member from said flow blocking position and is tapered to progressively diminish the passageway from said one passageway through said piston member as said piston member moves to the flow permitting position.

7. In apparatus for the logging of bore holes, the combination comprising a housing adapted to be lowered through a drill stem in a bore hole, logging apparatus within said housing, the lowermost end of said drill stem having a drill bit thereon, said housing having an extension on the lowermost end thereof, said extension having a exible medial section, a landing member at the lowermost end beneath said medial section adapted to contact said drill bit, the upper portion of the housing above said medial section being movable downwardly towards said landing member, said medial section being exible and movable outwardly when said housing comes to rest on said drill bit and said upper housing portion moves downwardly whereby the landing impact is cushioned, said medial section outward movement being such that the medial section contacts the inn-er wall of said drill stem to prevent ow through the space between said housing and the drill stem, and means for eifecting actuation of said logging apparatus in response to landing of the housing on the drill bit, said last-named means including a control means operable in response to the fluid pressure of the blocked uid for effecting said logging apparatus actuation.

8. Apparatus as claimed in claim 7 including an electrode assembly extending downwardly from said extension, the uppermost portion of said electrode assembly being contained within said extension.

9. Apparatus as claimed in claim 8 wherein said ex- `1 1 tension has a passageway means by-passing said medial section and said control means includes a piston member Within said passageway means and movableA from a position blocking flow therethrough to a position permitting ow therethrough.

10. Apparatus as claimed in claim 8 wherein said ex* tension has a lower section and an upper section joined by said medial section, said lower section being axially movable toward said upper section upon said outward movement of said medial section.

11. Apparatus as claimed in claim 10 including means cooperable with said upper and lower sections to support said lower section on said upper section and to limit separating movement thereof.

12. In apparatus for the logging of bore holes, the combination compr-ising a housing adapted to be lowered through a drill stem in a bore hole, logging apparatus within said housing, said housing having a section movable between a position permitting the ow of a fluid through the interior of the drill stem and a position blocking such fluid flow, means attached to said section for maintaining said section in said ow permitting position when the housing is lowered through the drill stem, means in the drill stem for restricting downward movement of said housing by contact therewith, means moving said section from said 110W opening position to said ow blocking position in response to contact of the lower end of said housing with said restricting means, means by-passing said section including a chamber in said housing and a pair of passageways communicating with the exterior of said housing and said chamber above and below said section, respectively, and a piston member in said chamber movable from a position blocking ow between said passageways to a position permitting flow between said passageways in response to the pressure build-up of the fluid flowing in the drill stem when said section has moved to said position thereof blocking the ilow of uid, and means connected to said piston member responsive to movement of said piston member from said flow blocking to said flow permitting position for effecting a control operation of said logging apparatus.

13. Apparatus as claimed in claim 12, wherein said logging apparatus control means comprises a control circuit for said logging apparatus, switching means connected in said control circuit for making and break-ing the same, said switching means having a switch contact mounted for movement through a switching movement to change the condition of said control circuit, and means interconnecting said switch contact and said piston member for actuating said switch contact through said switching movement thereof in response to said movement of said piston member.

14. In apparatus for the logging of bore holes, the combination comprising a housing adapted to be lowered through a drill stern in a bore hole, logging apparatus contained within said housing, and means secured to said housing for movement therewith for landing said logging apparatus and housing at the bottom of the drill stem and for initiating arming of said logging apparatus in response to the landing of said logging apparatus, said landing and arming means including means for blocking the ow of fluid through the drill stem in response to the landing of said housing at the bottom of the drill stern and means responsive to the uid pressure of the blocked uid for initiating arming of said logging apparatus.

15. In apparatus for the logging of bore holes, the combination comprising a housing adapted to be lowered through a drill stemv in a bore hole, logging apparatus within said housing, a casing connected to said housing having a movable section, means for moving said section into contact with the inner wall of the drill stem to block the How of uid passing through the interior of the drill stem in response to the landing of the housing at the bottom of the drill stem, said casing defining a chamber interiorly thereof communicating with the exterior thereof at locations above and below said section to receive fluid which passes through the drill stem and bypasses said section, pressure responsive piston means within said chamber below the uppermost of the locations of communication thereof with the exterior of the casing, said piston means being movable in response to the pressure developed by the blocking of fluid by said section from a rst position to a second position, and means including a control member connected to said piston means responsive to movement of-said piston means from said first to said second position for eifecting a control operation of said logging apparatus.